1. Field of the Invention
The present invention relates to a serial printer for printing print data by relatively moving print means and print medium in two directions orthogonal to each other, and a printing method for such a serial printer. More particularly, the invention relates to a print control system capable of printing an image of good quality even at the last line.
2. Discussion of the Related Art
Many types of serial printers, such as printers of the dot-impact type, thermal transfer type, ink-jet type, and the like, have been developed and practically used. Among those serial printers, the ink-jet printer, which jets ink against a print medium or a sheet of print paper by utilizing heat generated by a heating member to perform a printing operation, is capable of printing an image at high density. In this respect, the ink-jet printer is a promising printer.
In a conventional serial printer, all of the dots of the print head are used for printing, and the quantity of feeding of the sheet of print paper is determined depending on a preset line pitch and print data.
The way of feeding a sheet of print paper in a conventional printer is shown in FIG. 5. As shown, the sheet is fed by line-to-line or line pitch every time the print head prints one line. For a large line pitch, the quantity of the sheet feed is large, and for a small line pitch, the quantity of the sheet feed is small. Where the quantity of the sheet feed is not uniform, an error of the sheet feed tends to occur. When the print progresses, feed errors are accumulated. Accordingly, there is the possibility that in the printing operation of the lines near to the last line, one or some lines cannot be printed. Thus, in the conventional technique, where the quantity of feeding of the sheet is not uniform or fixed, the sheet is irregularly fed, leading to deterioration of the print quality.
In the printer of the type where the drive nozzles are individually controlled, the circuit must be arranged in accordance with the number of drive nozzles. Mere increase of the number of nozzles is impractical in light of the number of dots per line. Further, it is not easy to increase the number of nozzles.
When the remaining print area of the sheet of the print paper is smaller than the total number of dots of the print head, the conventional serial printer does not print at the last line, discharges the sheet, and prints the remaining print data on the next sheet. Thus, no print is carried out for the end portion of the sheet. The print area on the sheet cannot be utilized fully.
Japanese Patent Unexamined Publication No. Hei. 2-196672 discloses such a technique that to print the last line of the area to be printed, only the nozzles corresponding to the number of lines to be printed are selectively driven. To this end, in printing the last line, the quantity of the sheet feed is altered so as to allow the sheet to be fed by a distance corresponding to the number of lines to be printed. For this reason, irregular sheet feed tends to occur in the printing operation of the last line. Further, the effective print area handled in this disclosed technique ranges up to the mid location at the most on the sheet, not to the end portion of the sheet. No description referring to the print for the end portion is found. The technique also ineffectively uses the sheet.